1. Field of the Invention
The present invention relates to a display device formed using an element (light emitting element) which has a light-emitting material interposed between electrodes and emits light by applying current between the electrodes, and particularly, to a sealing structure of a light emitting element in such a display device.
2. Description of the Related Art
In recent years, a thin and lightweight display using a light emitting element has actively been developed. The light emitting element is formed by interposing a material which emits light by applying current between a pair of electrodes. A light source such as back light is not required since it itself emits light unlike in the case of liquid crystal, and the element itself is very thin. Therefore, it is extremely advantageous to form a thin and lightweight display.
Although the light emitting material of the light emitting element includes an organic one and an inorganic one, a light emitting element using an organic material that is driven with low voltage is often considered the most preferable. Drive voltage of a display having a light emitting element using an organic material is from 5 V to 10 V, and it is understood that it can be driven with very low voltage compared to an electroluminescent device using an inorganic material which requires drive voltage of from 100 V to 200 V. Drive voltage of a liquid crystal display singing the praises of low power consumption is approximately from 5 V to 15.5 V, and it is understood that the display having the light emitting element using an organic material can be driven with equal to or lower voltage than a liquid crystal display.
However, one background of not reaching a practical use yet while having such advantages is a problem of reliability. The light emitting element using an organic material often deteriorates due to moisture, and has a defect of being hard to obtain long-term reliability. The light emitting element which is deteriorated due to moisture causes decrease in luminance or does not emit light. It is conceivable that this causes a dark spot (black spot) and a shrink (decrease in luminance from an edge portion of a display device) in a display device using the light emitting element.
Various countermeasures are suggested to suppress such deterioration (for example, Reference 1: Japanese Patent Laid-Open No. 9-148066, and Reference 2: Japanese Patent Laid-Open No. 13-203076).
However, sufficient reliability is not obtained yet even when these countermeasures are taken, and thus, further improvement in reliability is expected.